Wireline formation testing is a process where a formation testing device is lowered into an open wellbore and positioned adjacent to the geological formation of interest. The device then seats a packer against the formation wall and forces a fluid extraction tube through the packer into the formation. Formation pressure is measured and a sample of formation fluids can then be extracted. Tool power and communication with surface telemetry is accomplished with a seven conductor wireline. Formation fluid samples are usually taken from points in the well in which previously recorded electrical logs indicate the possibility of hydrocarbons. Several liters of fluid ar, e typically taken. Currently, the composition of these fluid samples cannot be determined until the device is returned to surface.
A well that has been drilled for the purpose of producing hydrocarbons typically consists of a hole that is cylindrical in nature with diameters from a few inches to tens of inches and depths below the earth's surface ranging from a few hundred to tens of thousands of feet. After drilling has been completed electronic measurement devices are lowered into the well to record rock and fluid properties as a function of well depth for use in predicting the presence of hydrocarbons. Among these instruments is a formation testing device which is capable of extracting fluid samples from subsurface formations penetrated by the wellbore. Currently, the composition of these fluid samples cannot be determined until the formation testing device is returned to surface. A measurement technique has been developed to characterize a fluid sample in situ for fluid conductivity and, in some cases, hydrocarbon volume.
Numerous methods for measuring complex permittivity of fluids have been documented. These methods can typically be classified as transmission, resonance, or reflection in nature. Resonance type methods typically consist of measuring the quality factor of the cavity (Q and the resonant frequency of the cavity when filled with the fluid. This type of measurement is not well suited to extremely high conductivity measurements due to the Q of the cavity becoming very small. Reflection methods depend on a changing reflection coefficient or voltage sanding wave ratio as a lossy material is introduced as a line load or discontinuity. Again, this method yields poor accuracy for very high conductivities. Transmission type measurements where the lossy medium is substituted for some portion of the transmission line dielectric give the best results for high conductivity materials.
The TEM transmission line technique and the cavity technique for characterization of properties of materials such as formation fluid have been in use for a considerable period of time and have been extensively utilized for determination of hydrocarbon volume of formation fluid including other fluid constituents such as water and natural gas. One significant limitation for the determination of dielectric constant from resonant frequency lies in the fact that the Q of the testing cavity will be very low when completely filled with highly conductive fluids, hence determination of the conductivity will be very difficult. The usual technique (for lossy materials) is to place a very small sample in the testing cavity and to use perturbation techniques to determine the material properties.
The characterization of formation fluid for hydrocarbon volume as it enters a formation multi-tester instrument located downhole in fluid communication with a subsurface production formation of interest is considered a feature that would greatly enhance the effectiveness of the multi-tester instrument. The characterization of formation fluids should include measurement of the conductivity of water, often in the presence of hydrocarbons, under dynamic flow conditions.